1. Field of the Invention
The present invention relates to a method of and apparatus for analyzing a failure in semiconductor devices such as large scale integrated (LSI) devices.
2. Description of the Background Art
In semiconductor devices such as LSI devices, as the miniaturization of elements and the degree of integration increase, the number of interconnection levels of a metal interconnection structure increases. In high-performance LSI devices, with the increasing number of electrode pads, a so-called flip-chip structure in which electrode pads are formed not only around a chip but also in the chip has been mainstream. Such trends toward the increase in the number of interconnection levels of the metal interconnection structure and toward the flip-chip structure of the LSI devices make it impossible to conventionally analyze failures by accessing the chip (or wafer) through its upper surface by the use of a charged particle beam, such as an electron beam and an ion beam, or visible light. It is hence essential to employ failure analysis techniques which access the chip through its bottom surface (backside or opposite main surface from the device). An effective one of the failure analysis techniques of the backside accessing type includes a laser-induced current analysis (Infrared-Optical Beam Induced Current (IR-OBIC) analysis) technique utilizing a near-infrared laser beam. An example of the OBIC analyses by accessing the chip through its backside is disclosed in, for example, Japanese Patent Application Laid-Open No. 5-136240 (1993).
Light having energy not greater than the band gap energy of silicon, i.e. light having a wavelength of not less than 1 xcexcm can penetrate into a silicon substrate to some extent. The backside of the chip is irradiated with a near-infrared laser beam, and a change in current observed in synchronism with the scanning of the beam is converted into brightness to produce a current image. The IR-OBIC analysis obtains information about a failure-containing region in the chip, based on the current image.
The observed current is changed by photoexcitation and thermal excitation of electrons and holes which are caused by laser beam irradiation. Electron-hole pairs photoexcited near the pn junction in the silicon substrate are observed as photoinduced current to allow the manifestation of the pn junction, the detection of a junction leakage site, the detection of a gate leakage site, and the like. Selective photoexcitation of electrons or holes in metal interconnect lines allows the manifestation of a Schottky barrier. This permits the detection of in-process discrepancies, e.g. a faulty site at a contact between a metal interconnect line and the silicon substrate which results from the depletion of a dopant. On the other hand, the thermal excitation may be used to detect high-resistance sites such as voids and interface layers in the metal interconnect lines or contact holes. This utilizes the phenomenon that heat generated at a high-resistance site generates thermally-induced current and a resistance change, and a resultant change in observed current appears in the current image.
FIG. 17 is a block diagram of a background art apparatus for analyzing a failure in a semiconductor device. The background art apparatus, as shown in FIG. 17, comprises a laser beam source 101, a laser beam controller 102, a DC power supply 104, a current detector 105, a main controller 107, and a display 108. A laser beam source which generates a laser beam having a wavelength of about 1.1 xcexcm or about 1.3 xcexcm is commonly used as the laser beam source 101. When using the laser beam source 101 which generates the laser beam of about 1.1 xcexcm in wavelength, the apparatus can analyze all of the above-mentioned failure modes (i.e., a pn junction defect, a Schottky junction defect, and a faulty site in the metal interconnect line and the like). When using the laser beam source 101 which generates the laser beam of about 1.3 xcexcm in wavelength, the apparatus can analyze the Schottky junction defect and the faulty site in the metal interconnect line and the like among the above described three failure modes.
A conventional method of analyzing a failure by the use of the apparatus of FIG. 17 is described below. The laser beam source 101 generates a laser beam B101 based on a control signal S101 from the main controller 107. The laser beam controller 102 controls the path of the laser beam B101 based on a control signal S102 from the main controller 107, and scans a laser beam B102 across the backside of a sample 103. The current detector 105 detects current caused to flow in the sample 103 by the application of a predetermined voltage from the DC power supply 104 and the irradiation with the laser beam B102 from the laser beam controller 102, to input the detected current as data D101 to the main controller 107. Based on the data D101, the main controller 107 converts a change in current into brightness to produce a current image in the form of a two-dimensional image. The produced current image is inputted as data D102 to the display 108, and is then displayed on a screen of the display 108.
The background art apparatus and method can two-dimensionally determine a failure-containing region in a chip by reference to the produced current image. By reference to the current image only, however, it is difficult to specifically diagnose and localize a failure in the chip, that is, to determine where the failure occurs in the chip in three dimensions or whether the failure is the pn junction defect, the Schottky junction defect or the fault in the metal interconnect line.
A first aspect of the present invention is intended for a method of analyzing a failure. According to the present invention, the method comprises the steps of: (a) irradiating a sample with a laser beam; (b) detecting a current generated in the sample as a result of the irradiation with the laser beam; and (c) analyzing a failure in the sample, based on detection results obtained in the step (b) when the sample is irradiated with the laser beam at respective different wavelengths.
Preferably, according to a second aspect of the present invention, in the method of the first aspect, the sample is irradiated with laser beams of about 1.1 xcexcm, about 1.3 xcexcm, and not less than 2.0 xcexcm in wavelength, respectively, in the step (c).
Preferably, according to a third aspect of the present invention, in the method of the first aspect, the step (a) comprises the steps of: (a-1) scanningly irradiating the sample with the laser beam, and (a-2) fixedly irradiating a specific site of the sample with the laser beam, one of the steps (a-1) and (a-2) being selectively executed. The step (c) comprises the steps of: (c-1) determining a failure-containing region in which some form of failure occurs, based on a detection result obtained in the step (b) when the step (a-1) is executed; and (c-2) analyzing the cause of the failure in the failure-containing region, based on detection results obtained in the step (b) when the wavelength of the laser beam is changed while the failure-containing region is fixedly irradiated with the laser beam in the step (a-2).
Preferably, according to a fourth aspect of the present invention, in the method of the third aspect, the current is detected in the step (b) at a plurality of timed instants after irradiation of the failure-containing region with the laser beam, the plurality of timed instants being respectively corresponding to time constants of the current, the time constants being different from each other in excitation source of carriers generated by the irradiation with the laser beam.
A fifth aspect of the present invention is intended for a method of analyzing a failure. According to the present invention, the method comprises the steps of: (a) irradiating a sample with a laser beam of a predetermined wavelength; (b) applying a voltage to the sample; (c) detecting a current generated in the sample as a result of the application of the voltage and the irradiation with the laser beam; and (d) analyzing a failure in the sample, based on a detection result obtained in the step (b) when the voltage is changed while the sample is irradiated with the laser beam.
Preferably, according to a sixth aspect of the present invention, in the method of the fifth aspect, the step (a) comprises the steps of: (a-1) scanningly irradiating the sample with the laser beam; and (a-2) fixedly irradiating a specific site of the sample with the laser beam, one of the steps (a-1) and (a-2) being selectively executed. The step (d) comprises the steps of: (d-1) determining a failure-containing region in which some form of failure occurs, based on a detection result obtained in the step (c) when the step (a-1) is executed; and (d-2) analyzing the cause of the failure in the failure-containing region, based on a detection result obtained in the step (c) when the voltage is changed while the failure-containing region is fixedly irradiated with the laser beam in the step (a-2).
Preferably, according to a seventh aspect of the present invention, in the method of the third or sixth aspect, the sample is irradiated with the laser beam which is intermittently intercepted in the step (a-2).
Preferably, according to an eighth aspect of the present invention, in the method of the sixth or seventh aspect, the current is detected in the step (c) at a plurality of timed instants after irradiation of the failure-containing region with the laser beam, the plurality of timed instants being respectively corresponding to time constants of the current, the time constants being different from each other in excitation source of carriers generated by the irradiation with the laser beam.
A ninth aspect of the present invention is intended for a method of analyzing a failure. According to the present invention, the method comprises the steps of: (a) irradiating a sample with a laser beam of a predetermined wavelength; (b) detecting a current generated in the sample as a result of the irradiation with the laser beam at a plurality of timed instants after the irradiation of the sample with the laser beam, the plurality of timed instants being respectively corresponding to time constants of the current, the time constants being different from each other in excitation source of carriers generated by the irradiation with the laser beam; and (c) analyzing a failure in the sample, based on detection results obtained in the step (b).
A tenth aspect of the present invention is intended for an apparatus for analyzing a failure. According to the present invention, the apparatus comprises: a laser beam generator for selectively generating a plurality of laser beams of respective different wavelengths; a current detector for detecting a current generated in a sample as a result of irradiation with the laser beam; and a failure analyzer for analyzing a failure in the sample, based on a relationship between detection results from the current detector and the wavelengths.
Preferably, according to an eleventh aspect of the present invention, in the apparatus of the tenth aspect, the laser beam generator comprises a plurality of laser beam sources for generating the plurality of laser beams, respectively.
Preferably, according to a twelfth aspect of the present invention, in the apparatus of the tenth aspect, the laser beam generator comprises: a laser beam source for generating a laser beam of a predetermined wavelength; and a wavelength converter for converting the predetermined wavelength of the laser beam generated by the laser beam source to generate the plurality of laser beams.
Preferably, according to a thirteenth aspect of the present invention, in the apparatus of any one of the tenth to twelfth aspects, the plurality of laser beams include laser beams of about 1.1 xcexcm, about 1.3 xcexcm, and not less than 2.0 xcexcm in wavelength, respectively.
Preferably, according to a fourteenth aspect of the present invention, the apparatus of the tenth aspect further comprises a laser beam controller having a first function of scanningly irradiating the sample with the laser beam, and a second function of fixedly irradiating a specific site of the sample with the laser beam.
A fifteenth aspect of the present invention is intended for an apparatus for analyzing a failure. According to the present invention, the apparatus comprises: a laser beam generator for generating a laser beam of a predetermined wavelength; a voltage applier for applying a variable voltage to the sample; a current detector for detecting a current generated in the sample as a result of the application of the voltage and irradiation with the laser beam; and a failure analyzer for analyzing a failure in the sample, based on a relationship between a detection result from the current detector and the voltage.
Preferably, according to a sixteenth aspect of the present invention, the apparatus of the fifteenth aspect further comprises a laser beam controller having a first function of scanningly irradiating the sample with the laser beam, and a second function of fixedly irradiating a specific site of the sample with the laser beam.
Preferably, according to a seventeenth aspect of the present invention, in the apparatus of the fourteenth or sixteenth aspect, the specific site of the sample is a failure-containing region in which some form of failure occurs. The apparatus further comprises a laser beam interceptor for intermittently intercepting the laser beam when the laser beam controller fixedly irradiates the failure-containing region with the laser beam.
Preferably, according to an eighteenth aspect of the present invention, in the apparatus of any one of the fourteenth, sixteenth and seventeenth aspect, the current detector detects the current at a plurality of timed instants after irradiation of the failure-containing region with the laser beam, the plurality of timed instants being respectively corresponding to time constants of the current, the time constants being different from each other in excitation source of carriers generated by the irradiation with the laser beam.
In accordance with the first aspect of the present invention, the method uses the plurality of laser beams differing in wavelength from each other for failure analysis to achieve the analysis of the cause of the failure in the sample and the three-dimensional analysis of a failure site in the sample.
In accordance with the second aspect of the present invention, the method can analyze three types of failure, i.e. a pn junction defect, a Schottky junction defect, and a faulty site in a metal interconnect line, in a semiconductor device employing a silicon substrate.
In accordance with the third aspect of the present invention, the method can determine the failure-containing region by scanningly irradiating the sample with the laser beam, and thereafter analyze the cause of the failure in the failure-containing region by fixedly irradiating only the failure-containing region with the laser beam and converting the wavelength of the laser beam.
In accordance with the fourth aspect of the present invention, the method can analyze the presence or absence of the cause of the failure of the three types at the timed instants at which the occurrence of the failure significantly affects a variation in current value.
In accordance with the fifth aspect of the present invention, changing the voltage applied to the sample while irradiating the sample with the laser beam allows the analysis of the cause of the failure in the sample and the three-dimensional analysis of the failure site in the sample.
In accordance with the sixth aspect of the present invention, the method can determine the failure-containing region by scanningly irradiating the sample with the laser beam, and thereafter analyze the cause of the failure in the failure-containing region by fixedly irradiating only the failure-containing region with the laser beam and changing the applied voltage.
In accordance with the seventh aspect of the present invention, the method can avoid damages to the sample due to the continuous irradiation with the laser beam.
In accordance with the eighth aspect of the present invention, the method can analyze the presence or absence of the cause of the failure of the three types at the timed instants at which the occurrence of the failure significantly affects a variation in current value.
In accordance with the ninth aspect of the present invention, the method can analyze the presence or absence of the cause of the failure of the three types at the timed instants at which the occurrence of the failure significantly affects a variation in current value, and achieves the analysis of the cause of the failure in the sample and the three-dimensional analysis of the failure site in the sample by the use of the single-wavelength laser beam.
In accordance with the tenth aspect of the present invention, the apparatus uses the plurality of laser beams differing in wavelength from each other for failure analysis to achieve the analysis of the cause of the failure in the sample and the three-dimensional analysis of the failure site in the sample.
In accordance with the eleventh aspect of the present invention, the apparatus comprises the plurality of laser beam sources to provide the laser beams differing in wavelength from each other from the respective laser beam sources.
In accordance with the twelfth aspect of the present invention, the wavelength converter converts the wavelength of the laser beam to eliminate the need to provide individual laser beam sources for providing the laser beams differing in wavelength from each other, thereby simplifying the construction of the apparatus.
In accordance with the thirteenth aspect of the present invention, the apparatus can analyze three types of failure, i.e. a pn junction defect, a Schottky junction defect, and a faulty site in a metal interconnect line, in a semiconductor device employing a silicon substrate.
In accordance with the fourteenth aspect of the present invention, the apparatus can determine the failure-containing region in which some form of failure occurs by scanningly irradiating the sample with the laser beam, and analyze the cause and site of the failure in the failure-containing region by fixedly irradiating the failure-containing region with the laser beam and converting the wavelength of the laser beam.
In accordance with the fifteenth aspect of the present invention, changing the voltage applied to the sample while irradiating the sample with the laser beam allows the analysis of the cause of the failure in the sample and the three-dimensional analysis of the failure site in the sample.
In accordance with the sixteenth aspect of the present invention, the apparatus can determine the failure-containing region in which some form of failure occurs by scanningly irradiating the sample with the laser beam, and analyze the cause and site of the failure in the failure-containing region by fixedly irradiating the failure-containing region with the laser beam and changing the applied voltage.
In accordance with the seventeenth aspect of the present invention, the apparatus can avoid damages to the sample due to the continuous irradiation with the laser beam.
In accordance with the eighteenth aspect of the present invention, the apparatus can analyze the presence or absence of the cause of the failure of the three types at the timed instants at which the occurrence of the failure significantly affects a variation in current value.
It is therefore an object of the present invention to provide a method of analyzing failure which can diagnose and localize a failure in a sample only by reference to a current image produced by laser beam irradiation, and an apparatus for analyzing a failure which can implement the method.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.